The c-myb oncogene is expressed at high levels in immature hematopoietic cells and in many leukemias. Leukemic cells appear to be more sensitive to antisense inhibition of c-myb expression than normal hematopoietic cells are. Although it is clear that leukemic cells require increased c-myb expression for proliferation, the molecular mechanisms that lead to this increased expression are not known. The goal of this proposal is to determine the molecular mechanisms responsible for the transcriptional control of the c-myb gene in both normal and malignant hematopoietic cells. 1. Identification of the molecular mechanisms of transcriptional control of c-myb in normal T cells. Activation of T cells causes increased expression of c-myb mRNA. They will perform in vivo footprinting, in vitro protein-DNA binding studies, and transient transfection experiments to study the transcriptional regulation of the c-myb gene. 2. Identification of the molecular mechanism of transcriptional control of c-myb in leukemic cells. Studies as described in Aim 1 will be performed on leukemic samples that express high levels of c-myb mRNA and cell lines will be used for the transient transfection experiments. The regulatory proteins identified in leukemic cells will be compared to those identified in normal T cells. 3. Role of the first intron in the transcriptional control of c-myb. They have shown that a positive regulatory region exists in the first intron. They will continue to study this and also investigate the role it plays in leukemic cells. They will also determine whether the block to transcription elongation is in the first intron or at the transcription start site. 4. Determination of the methylation status of c-myb. Methylation of CpG dinucleotides is thought to be involved in a gene silencing mechanism. They will determine the methylation status of c-myb in both quiescent and activated T cells, in HeLa cells which do not express c-myb, and in leukemic cells. With this information they hope to discover how c-myb expression is deregulated in leukemias and to begin to understand how this contributes to malignant transformation.